Abstract
The hypothesis that individuality is a derived trait in animals (Buss, '87, The Evolution of Individuality, Princeton, NJ: Princeton University Press; Michod, '99, Darwinian Dynamics, Princeton, NJ: Princeton University Press) can be further tested by a βtreeβbasedβ analysis utilizing a comparative methodology and recent phylogenies. We conducted a maximum parsimony analysis in which we mapped character states for clonality, coloniality, and mode of germline development onto four recent phylogenetic hypotheses (Peterson and Eernisse, 2001, Evol Dev 3:170β205). Clonality appears to be a shared primitive character for metazoans. Coloniality, on the other hand, is a derived trait found in relatively few phyla. The germline appears to have been derived at or near the origin of the first bilaterians. The stemβlineage metazoan thus appears to have been a clonal, acolonial organism that exhibited somatic embryogenesis. The stemβlineage bilaterian also was likely clonal and acolonial. Nevertheless, this lineage likely exhibited preformation, i.e., its germline was determined during embryonic development. In addition to supporting the hypothesis that the germline is a derived feature in animals, this analysis is relevant to current debates concerning the nature of the latest common ancestor of the bilaterians. J. Exp. Zool. (Mol. Dev. Evol.) 297B: 35β47, 2003. Β© 2003 WileyβLiss, Inc.